Vaso-occlusive devices are implants that are placed in cavities within a patient's vasculature, e.g., within an aneurysm located in the vasculature of the brain. The devices are typically implanted using a delivery catheter that is advanced endoluminally to the treatment site.
An example of a well-known vaso-occlusive device has an elongated helically-wound “primary shape” when constrained within a delivery catheter, and a three-dimensional “secondary” shape once deployed from the catheter and left, more or less, unconstrained in the implantation site. Because of the helical primary shape, these devices are generally referred to as vaso-occlusive devices. The coils are typically made of a very soft and flexible metal, e.g., a platinum alloy. Depending on the size and/or shape of the aneurysm, one or more occlusive coils may be implanted in order to reduce the risk of the aneurysm growing and/or rupturing. The vaso-occlusive coils may also promote embolization of the aneurysm.
To manufacture the vaso-occlusive coils, a wire comprising the coil material is first wound around a small diameter, primary mandrel and heated to produce the helical primary shape. The primary shape coil is then wrapped around a larger diameter secondary mandrel, which is heated to set the secondary shape into the primary shape coil.
One disadvantage of this process is that the secondary windings (which are larger loops formed by the elongate primary coil) often overlap one another as the primary shape coil is wound onto or around the secondary mandrel. In particular, kinks and abrupt bends can form in the coil as a result of overlapping winding around the secondary mandrel, and can become “programmed” into the secondary shape of the coil during heat treatment. These kinks and bends can increase frictional resistance of the coil as it is advanced through a delivery catheter, requiring greater force to deploy the coil into the aneurismal cavity. Kinks and bends can also cause problems in the event a coil that is partially deployed needs to be withdrawn from the body, as they can more readily snag other deployed coils at the site. Additionally, uneven or overlapping secondary windings can result in coils that impart greater stresses on aneurysm walls, increasing the chance the aneurysm wall can be damaged or burst.